In a conventional micro-hybrid system with regenerative braking, problems may exist in recovering efficiently the energy produced during braking phases of the motor vehicle.
This energy recovery is affected in particular by the type of energy storage unit used.
In general, in a micro-hybrid system, a rotary electrical machine and an electrochemical battery supply the electrical consumers via an electrical distribution network of the vehicle.
The rotary electrical machine, which can function as an alternator, is also designed to recharge the battery via a regulation device.
Typically, when the thermal engine of the vehicle is functioning, the alternator supplies the electrical consumers and charges the battery. When the alternator is not discharging current, the battery supplies all the electric energy the vehicle needs.
When the vehicle is in a transitory braking phase, a large quantity of kinetic energy can be recovered.
It then becomes highly advantageous to transform this kinetic energy into electric energy, in order to use it in the electrical distribution network.
Systems are known which permit direct supply, to certain electrical consumers, of the energy which is recovered by braking.
Other systems also permit supply to the battery of the said recovered energy, so as to charge the said battery.
From the point of view of the battery, this charge corresponds to an increase in a regulation set point imposed by the regulation device.
However, according to a first aspect, the battery cannot be subjected to an excessively high regulation set point because of the risk of accelerated deterioration of its state of health (SOH).
In usual conditions, this regulation set point is dependent on the temperature of the battery. For example, for a lead battery, and with use of voltage regulation, the regulation set point is approximately 14.3 V at a temperature of approximately 20° C. inside the battery.
In addition, for this lead battery, the maximum voltage admissible is contained in an interval of approximately 15V to approximately 16V.
This results in a maximum variation of voltage contained in an interval of approximately 0.7V to approximately 1.7V.
That leads to a relatively low current entering the battery, and thus, during braking phases, to a relatively limited quantity of energy recovered from the battery, particularly in comparison with the energy which is produced during these phases.
According to a second aspect, the battery cannot receive an excessively large quantity of energy transitorily, which for example results in variation of voltage of approximately 5V.
In fact, if the battery has voltage of approximately 10V, charging of the battery during a braking phase, which corresponds to a regulation set point command of approximately 15V, could damage the state of health of the battery, and in particular irreversibly.
Consequently, in these micro-hybrid systems, there may be problems of efficiency of the so-called regenerative braking function, with this function being affected by an energy state of the battery.
There is therefore a need to improve the regenerative braking function reliably, simply and in a standard manner at least for battery technology, and thus to reinforce the performance of the micro-hybrid systems.